It is possible to abruptly withdraw narcotics post-operatively from addicted patients, in whom specific thalamic lesions had been made for the treatment of intractable pain, with no evidence of narcotic withdrawal. These same areas of the thalamus will be studied in addicted rats by means of chronic indwelling electrodes. The rats will be addicted by controlled intravenous administration of morphine, and the addiction maintained by self-administration lever pressing. Neurophysiologic activity of parts of the brain concerned with pain perception will be monitored during development of morphine tolerance and during narcotic withdrawal. An attempt will be made to control the effects of addiction by making lesions in these areas.